Introduction: Turning means that lathe processing is a part of mechanical processing. Lathe processing mainly uses turning tools to turn rotating workpieces. Lathes are mainly used to process shafts, disks, sleeves and other workpieces with rotating surfaces, and are the most widely used type of machine tool processing in machinery manufacturing and repair factories.
The skills of a turner are endless, and the most common turner does not need too high a skill. It can be divided into 5 types of car workers, which are the most common in society at present.
1. Ordinary mechanical lathe workers are easy to learn. Find a lathe processing department, which is better than what you learned in school
2. Mold turning workers, especially plastic mold precision turning workers! Strict requirements on tools and precise dimensions
You need to know what kind of steel has a good glazing effect, that is, the mirror surface
Is the product of this set of molds made of abs or other materials? How much is the stretchability of the plastic parts === A lot of common knowledge, plasticine is an essential tool for this kind of car workers! ! !
The finish of the car should be good, easy to polish, and achieve a mirror effect. It needs a plastic mold foundation. 4 claws are very commonly used. Generally, several templates are added together to car. Knowledge of plastic mold threads must be mastered! The difficulty is higher!
3. Cutting tool turning, processing reamers, drills, alloy cutterheads == cutting tool stems, this kind of turning is the simplest, best and most tiring
It is usually mass-produced, and the most commonly used ones are double tops, turning taper, and flow modulus. It is the fastest and easiest way to minimize tool wear, because the hardness of this kind of turning products is no better than your white How much lower is the steel knife! How well your alloy knife is sharpened will completely affect your grades! !
4. Lathe workers for large equipment, this kind of lathe workers must have experienced skills, young people basically dare not drive! !
When using a vertical car, I teach more. example:
To turn a crankshaft, you have to look at the drawing repeatedly n times first, which one is turned first and which is turned last, whether it is the amount of lost wear, or directly processed to size, whether the thread is positive or negative... === Some advanced techniques
5. CNC lathe, this kind of lathe is the simplest but also the most difficult. First of all, you must be able to read drawings, program, conversion formulas, and tool applications! ! !
As long as you master the lathe theory and have certain knowledge of mathematics, mechanics and cad, you can learn it quickly.
Turning
It is to change the shape and size of the blank by using the rotary motion of the workpiece and the linear or curved motion of the tool on the lathe, and process it to meet the requirements of the drawing.
Turning is a method of cutting a workpiece on a lathe by using the rotation of the workpiece relative to the tool. The cutting energy for turning operations is primarily provided by the workpiece rather than the tool. Turning is the most basic and common cutting processing method, which occupies a very important position in production. Turning is suitable for machining rotary surfaces. Most workpieces with rotary surfaces can be processed by turning methods, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, end faces, grooves, threads, and rotary forming surfaces. The tools used are mainly turning tools.
Among all kinds of metal cutting machine tools, lathes are the most widely used category, accounting for about 50% of the total number of machine tools. The lathe can not only turn the workpiece with a turning tool, but also perform drilling, reaming, tapping and knurling operations with drill bits, reamers, taps and knurling knives. According to different process characteristics, layout forms and structural characteristics, lathes can be divided into horizontal lathes, floor lathes, vertical lathes, turret lathes and profiling lathes, etc., most of which are horizontal lathes
security technical issues
Turning is the most widely used in the machine manufacturing industry. There are a large number of lathes, a large number of personnel, a wide range of processing, and a variety of tools and fixtures used. Therefore, the safety technical issues of turning processing are particularly important. , its key work is as follows:
1. Chip damage and protective measures. All kinds of steel parts processed on the lathe have good toughness, and the chips generated during turning are full of plastic curl and have sharp edges. When cutting steel parts at high speed, red hot and long chips will be formed, which can easily hurt people. At the same time, they are often wrapped around the workpiece, turning tool and tool holder. Therefore, iron hooks should be used to clean or break them in time during work. It should be stopped and removed, but it is absolutely not allowed to remove or break it by hand. In order to prevent chip damage, measures to break chips, control chip flow and add various protective baffles are often taken. The chip breaking measure is to grind a chip breaker or a step on the turning tool; use an appropriate chip breaker and mechanically clamp the tool.
2. The clamping of the workpiece. During the turning process, there are many accidents in which the machine tool is damaged, the tool is broken or smashed, and the workpiece falls or flies out due to improper clamping of the workpiece. Therefore, in order to ensure the safe production of turning processing, special attention must be paid when clamping workpieces. For parts of different sizes and shapes, appropriate fixtures should be selected, and the connection between three-jaw, four-jaw chucks or special fixtures and the main shaft must be stable and reliable. The workpiece should be clamped and clamped. The large workpiece can be clamped with a sleeve to ensure that the workpiece does not shift, fall off or be thrown out when it rotates at high speed and is cut under force. If necessary, it can be strengthened and fixed by the center frame and the center frame. Remove the wrench immediately after snapping.
3. Safe operation. Before work, the machine tool should be fully inspected, and it can be used only after confirming that it is in good condition. The clamping of the workpiece and the cutting tool ensures that the position is correct, firm and reliable. During processing, when changing tools, loading and unloading workpieces and measuring workpieces, the machine must stop. The workpiece must not be touched by hand or wiped with cotton silk when it is rotating. It is necessary to properly select the cutting speed, feed rate and labor depth, and overload processing is not allowed. Workpieces, fixtures and other sundries are not allowed to be placed on the head of the bed, the tool rest and the bed. When using the file, move the turning tool to a safe position, with the right hand in front and the left hand behind, to prevent the sleeve from being entangled. The machine tool must be used and maintained by a special person, and other personnel are not allowed to use it.
2 Notes
The processing technology of CNC lathe is similar to that of ordinary lathe, but since the CNC lathe is a one-time clamping and continuous automatic processing completes all the turning processes, the following aspects should be paid attention to.
1. Reasonable selection of cutting amount:
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For high-efficiency metal cutting, the material to be processed, cutting tools, and cutting conditions are three major elements. These determine machining time, tool life and machining quality. An economical and effective processing method must be a reasonable choice of cutting conditions. The three elements of cutting conditions: cutting speed, feed rate and depth of cut directly cause damage to the tool. With the increase of cutting speed, the temperature of the tool tip will rise, which will cause mechanical, chemical and thermal wear. Cutting speed increased by 20%, tool life will be reduced by 1/2. The relationship between feed conditions and tool back wear occurs within a very small range. However, the feed rate is large, the cutting temperature rises, and the wear behind is large. It has less effect on the tool than cutting speed. Although the effect of depth of cut on the tool is not as large as the cutting speed and feed rate, when cutting with a small depth of cut, the material to be cut will produce a hardened layer, which will also affect the life of the tool. The user should choose the cutting speed to use according to the material to be processed, hardness, cutting state, material type, feed rate, cutting depth, etc. The selection of the most suitable processing conditions is selected on the basis of these factors. Regular, steady wear to the end of life is the ideal condition. However, in actual operation, the choice of tool life is related to tool wear, size change, surface quality, cutting noise, processing heat, etc. When determining the processing conditions, it is necessary to conduct research according to the actual situation. For difficult-to-machine materials such as stainless steel and heat-resistant alloys, coolant can be used or a rigid cutting edge can be used.
2. Reasonable choice of knives:
(1) When roughing, it is necessary to choose a tool with high strength and good durability, so as to meet the requirements of large cutting capacity and large feed rate during rough turning.
(2) When finishing the car, it is necessary to choose a tool with high precision and good durability to ensure the requirements of machining accuracy.
(3) In order to reduce the tool change time and facilitate tool setting, machine-clamped tools and machine-clamped blades should be used as much as possible.
3. Reasonable selection of fixtures:
(1) Try to use general fixtures to clamp workpieces, and avoid using special fixtures;
(2) Part positioning datum coincides to reduce positioning error.
4. Determine the processing route: The processing route refers to the movement track and direction of the tool relative to the part during the machining process of the CNC machine tool.
(1) It should be able to ensure the machining accuracy and surface roughness requirements;
(2) The processing route should be shortened as much as possible to reduce the idle travel time of the tool.
5. The relationship between processing route and processing allowance:
At present, under the condition that the CNC lathe has not yet been widely used, generally the excessive allowance on the blank, especially the allowance containing forged and cast hard skin layers, should be processed on the ordinary lathe. If it must be processed with a CNC lathe, attention should be paid to the flexible arrangement of the program.
6. Fixture installation points:
At present, the connection between the hydraulic chuck and the hydraulic clamping cylinder is realized by the pull rod. The key points of hydraulic chuck clamping are as follows: first, use a wrench to remove the nut on the hydraulic cylinder, remove the pull tube, and pull it out from the rear end of the main shaft, and then Use a wrench to remove the chuck fixing screw to remove the chuck
3 General Rules
Turning general process code (JB/T9168.2-1998)
Clamping of turning tools
1) The tool holder of the turning tool should not be too long to protrude from the tool holder, and the general length should not exceed 1.5 times the height of the tool holder (except for turning holes, grooves, etc.)
2) The centerline of the tool holder of the turning tool should be perpendicular or parallel to the direction of the cutting tool.
3) Adjustment of the height of the tool tip:
(1) When turning the end face, turning the conical surface, turning the thread, turning the forming surface and cutting the solid workpiece, the tip of the tool should generally be at the same height as the axis of the workpiece.
(2) The rough turning outer circle, finishing turning hole, and tool tip should generally be slightly higher than the axis of the workpiece.
(3) When turning slender shafts, rough holes, and cutting hollow workpieces, the tip of the tool should generally be slightly lower than the axis of the workpiece.
4) The bisector of the nose angle of the thread turning tool should be perpendicular to the axis of the workpiece.
5) When clamping the turning tool, the gaskets under the tool bar should be few and flat, and the screws pressing the turning tool should be tightened.
Workpiece clamping
1) When using a three-jaw self-centering chuck to clamp the workpiece for rough turning or finishing turning, if the diameter of the workpiece is less than 30mm, the overhang length should not be more than 5 times the diameter; if the workpiece diameter is greater than 30mm, the overhang length The length should not be greater than 3 times the diameter.
2) When clamping irregular heavy workpieces with four-jaw single-action chucks, faceplates, angle irons (bent plates), etc., a counterweight must be added.
3) When machining shaft workpieces between the tops, adjust the axis of the top of the tailstock to coincide with the axis of the lathe spindle before turning.
4) When machining a slender shaft between two centers, a steady tool rest or a center rest should be used. Pay attention to adjust the top tightening force during processing, and pay attention to lubrication of the dead center and the steady frame.
5) When using the tailstock, the sleeve should be extended as short as possible to reduce vibration.
6) When clamping a workpiece with a small supporting surface and a high height on the vertical lathe, the raised jaws should be used, and a pull rod or a pressure plate should be added at an appropriate position to compress the workpiece.
7) When turning wheel and sleeve castings and forgings, alignment should be done according to the unprocessed surface to ensure uniform wall thickness of the processed workpiece.
Turning
1) When turning the stepped shaft, in order to ensure the rigidity during turning, generally the part with larger diameter should be turned first, and the part with smaller diameter should be turned later.
2) When grooving on the workpiece of the shaft, it should be carried out before finishing turning to prevent deformation of the workpiece.
3) When finishing the threaded shaft, generally the non-threaded part should be finished after thread processing.
4) Before drilling, the end surface of the workpiece should be turned flat. If necessary, the center hole should be punched first.
5) When drilling a deep hole, generally drill the pilot hole first.
6) When turning (Φ10-Φ20) mm holes, the diameter of the tool holder should be 0.6-0.7 times the diameter of the machined hole; when machining holes with a diameter larger than Φ20 mm, generally a tool holder with a clamping head should be used.
7) When turning multi-start threads or multi-start worms, try cutting after adjusting the exchange gear.
8) When using an automatic lathe, it is necessary to adjust the relative position of the tool and the workpiece according to the machine tool adjustment card. After the adjustment, it is necessary to carry out trial turning, and the first piece is qualified before processing; pay attention to the wear of the tool and the size and surface roughness of the workpiece at any time during the processing Spend.
9) When turning on a vertical lathe, when the tool holder is adjusted, the beam must not be moved arbitrarily.
10) When the relevant surface of the workpiece has a position tolerance requirement, try to complete the turning in one clamping.
11) When turning cylindrical gear blanks, the hole and the reference end surface must be processed in one clamping. If necessary, the marking line should be drawn near the gear index circle on the end face.
44 error compensation
Modern machinery manufacturing technology is developing towards high efficiency, high quality, high precision, high integration and high intelligence. Precision and ultra-precision machining technology has become the most important component and development direction of modern machinery manufacturing, and has become a key technology for improving international competitiveness. With the wide application of precision machining, turning machining error has become a hot research topic. Since thermal errors and geometric errors account for most of the various errors of machine tools, reducing these two errors, especially the thermal errors, has become the main goal. Error Compensation Technology (ECT for short) appears and develops with the continuous development of science and technology. Losses caused by thermal deformation of machine tools are considerable. Therefore, it is extremely necessary to develop a high-precision, low-cost thermal error compensation system that can meet the actual production requirements of the factory to correct the thermal error between the spindle (or workpiece) and the cutting tool, so as to improve the machining accuracy of the machine tool, reduce waste products, increase production efficiency and economic benefits.
Basic definition and characteristics of error compensation
basic definition
The basic definition of error compensation is to artificially create a new error to offset or greatly weaken the original error that is currently a problem. The resulting error and the original error are equal in value and opposite in direction, thereby reducing machining error and improving the dimensional accuracy of the part.
The earliest error compensation was realized by hardware. Hardware compensation is a mechanical fixed compensation. To change the compensation amount when the error of the machine tool changes, it is necessary to re-make parts, calibration scales or re-adjust the compensation mechanism. Hardware compensation has the disadvantages of being unable to solve random errors and lacking flexibility. The feature of the software compensation developed recently is that the advanced technology and computer control technology of various contemporary disciplines are used comprehensively to improve the machining accuracy of the machine tool without any changes to the machine tool itself. Software compensation overcomes many difficulties and shortcomings of hardware compensation, and pushes the compensation technology to a new stage.
characteristic
Error compensation (technology) has two main characteristics: scientific and engineering.
The rapid development of scientific error compensation technology has greatly enriched the theory of precision mechanical design, precision measurement and the entire precision engineering, and has become an important branch of this discipline. Technologies related to error compensation include detection technology, sensing technology, signal processing technology, photoelectric technology, material technology, computer technology and control technology. As a branch of new technology, error compensation technology has its own independent content and characteristics. It will be of great scientific significance to further study error compensation technology and make it theoretical and systematized.
The engineering significance of engineering error compensation technology is very significant, and it contains three meanings: first, the use of error compensation technology can easily achieve the level of accuracy that "hard technology" can only achieve at a great cost; second, the use of error compensation Technology can solve the precision level that "hard technology" usually can't achieve; third, if the error compensation technology is used to meet certain precision requirements, the cost of instrument and equipment manufacturing can be greatly reduced, with
There are very significant economic benefits.
Generation and Classification of Thermal Errors in Turning
With the further improvement of the precision requirements of machine tools, the proportion of thermal error in the total error will continue to increase, and the thermal deformation of machine tools has become the main obstacle to improve machining accuracy. Machine tool thermal errors are mainly caused by thermal deformation of machine tool components caused by internal and external heat sources such as motors, bearings, transmission parts, hydraulic systems, ambient temperature, and coolant. The geometric error of the machine tool comes from the manufacturing defects of the machine tool, the fit error between the machine tool components, the dynamic and static displacement of the machine tool components, and so on.
Basic method of error compensation
In summary and related references, it can be known that turning errors are generally caused by the following factors:
Machine tool thermal deformation error;
Geometric errors of machine tool parts and structures;
Errors caused by cutting forces;
Tool wear error;
Other error sources, such as the servo error of the machine tool shaft system, the error of the NC interpolation algorithm, and so on.
There are two basic methods to improve machine tool accuracy: error prevention method and error compensation method.
The error prevention method is an attempt to eliminate or reduce possible error sources through design and manufacturing approaches. The error prevention method is effective to reduce the temperature rise of the heat source, balance the temperature field and reduce the thermal deformation of the machine tool to a certain extent. But it is impossible to completely eliminate thermal deformation, and the cost is very expensive;
The application of thermal error compensation law opens up an effective and economical way to improve the accuracy of machine tools.
Related conclusions
The research on turning machining error is the most important component and development direction of modern machinery manufacturing, and has become a key technology to improve international competitiveness. skills requirement.
The error compensation technology can meet the high precision and low cost of the actual production requirements of the factory. The thermal error compensation technology can correct the thermal drift error between the spindle (or workpiece) and the cutting tool, improve the machining accuracy of the machine tool, reduce waste products, increase production efficiency and economy benefit.
5 Frequently Asked Questions
When ordinary lathes turn large-pitch threads powerfully, sometimes the saddle will vibrate. If it is light, it will cause ripples on the machined surface, and if it is severe, it will break the knife. When cutting, students often have the phenomenon of stabbing or breaking the knife. There are many reasons for the above problems. Now we mainly discuss this phenomenon and its solution through the analysis of the force of the tool.
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1 The origin and cause of the problem
We know that when turning a thread with a small pitch, the straight-feed cutting method is generally used (feeding in a straight line perpendicular to the axis of the workpiece); when turning a thread with a large pitch, in order to reduce the cutting force, the left and right borrowing is often used Cutting method (by moving the small slide to let the thread turning tool cut with the left and right cutting edges respectively).
When turning threads, the movement of the saddle is realized by the rotation of the long lead screw to drive the movement of the split nut. There is an axial clearance at the bearing of the long screw, and there is also an axial clearance between the long screw and the split nut. When using the left and right borrowing cutting method to forcefully turn the right-handed worm with the right main cutting edge, the tool bears the force P given by the workpiece (ignoring the friction between the chip and the rake face, as shown in Figure 1), and the force P is decomposed into The axial component force Px and the radial component force are combined, wherein the axial component force Px is the same as the feed direction of the tool, and the tool transmits the axial component force Px to the bed saddle, thus pushing the bed saddle to the side where there is a gap Do fast and violent back and forth movement, the result is to make the tool move back and forth, and cause ripples on the machined surface, or even break the knife. However, there is no such phenomenon when cutting with the left main cutting edge. When cutting with the left main cutting edge, the axial component force Px borne by the tool is opposite to the feed direction, and moves in the direction of eliminating the gap. At this time, the bed saddle moves at a constant speed. .
When cutting, the movement of the middle slide plate is realized by the rotation of the lead screw of the middle slide plate to drive the movement of the nut. There is an axial clearance at the bearing of the lead screw, and there is also an axial clearance between the lead screw and the nut. When cutting on a lathe, the tool rake face (with rake angle) bears the force P given by the workpiece (ignoring the friction between the chip and the rake face, as shown in Figure 2), and the force P is decomposed into force Pz and Radial force component, in which the radial force component is the same as the cutting tool’s feed direction, pointing to the workpiece, pushing the tool towards the workpiece, which will pull the middle slide to move in the direction of the gap, causing the cutting knife to suddenly pierce the hand parts, resulting in piercing (breaking) of the knife or bending of the workpiece.
2 solutions
When the turning pitch is large and the thread is cut with the left and right cutting method, in addition to adjusting the relevant parameters of the lathe, the matching gap between the saddle and the guide rail of the bed should also be adjusted to make it slightly tighter to increase the movement. The friction force can reduce the possibility of the saddle moving, but the gap should not be adjusted too tight, so that the saddle can be shaken smoothly.
Adjust the clearance of the middle slide to minimize the clearance; adjust the tightness of the small slide to make it slightly tighter to prevent the turning tool from shifting during turning. The protruding length of the workpiece and the tool bar should be shortened as much as possible, and the left main blade should be used for cutting as much as possible; when cutting with the right main blade, the amount of back cutting should be reduced; the rake angle of the right main blade should be increased, and the edge of the blade should be straight and sharp. , in order to reduce the axial component force Px that the tool bears. In theory, the larger the rake angle of the right main blade, the better.
